A fundamental feature of most network communications, including the Internet, is the layered approach to transmission protocol based on the OSI reference model. Equally fundamental is the concept of transmitting information in piecemeal fashion through packetized data, or “packets”. In order for two devices to exchange packets of information across a network, each packet includes a header. The header contains information that defines the connection. In a network using the TCP/IP protocol stack, for example, a connection typically is defined at a minimum by information relating to OSI layers 3 (network) and 4 (transport). Typically five pieces of information define the connection: IP source address, IP destination address, IP protocol, TCP source port, and TCP destination port.
The information defining the connection is typically contained in fields within the packet header, and these fields can fall in different positions and may have different lengths within the header, depending on the protocols and protocol versions used by the various layers. Thus, extracting the fields that define a connection is not a trivial process. Prior art systems have used a processor associated with the logical device receiving or sending communications to decode and extract connection information. This processor-based approach is time-consuming and decreases processor availability for other tasks, especially where a single logical device may monitor and extract header fields from incoming messages of multiple active connections.
An alternate approach to extract header fields unburdens the processor by using dedicated hardware to extract connection data from header fields. One problem with such an approach is that dedicated hardware cannot adapt to new protocols and header configurations, unlike a programmable general purpose processor, which can adapt to new header topography through software modifications.